WASHINGTON — China's power and North Korea's erratic belligerence loom as the greatest challenges for America in the Pacific, said Adm. Robert F. Willard, tapped by the Obama administration to head Honolulu-based U.S. Pacific Command.

"We are rightly concerned about the situation in North Korea," Willard told the Senate Armed Services Committee yesterday at his confirmation hearing.

Willard has commanded the U.S. Pacific Fleet since May 2007, a position held by Adm. Chester Nimitz during World War II.

He said the motivations behind North Korea's recent atomic bomb and missile tests, which prompted the U.S. Navy to fortify defenses near Hawai'i, "remain something of a mystery." Still, Willard said, "we continue to posture for these, and try to control their behavior."

President Obama and Defense Secretary Robert Gates nominated the former "top gun" naval aviator in May to lead the Pacific Command at Camp Smith, the largest of the U.S. military commands, and one of the most complicated.

If confirmed by the Senate, Willard would succeed Adm. Timothy Keating in the fall. Keating, who was appointed to the Pacific's top military job in 2007, is retiring.

Willard's confirmation seemed on track yesterday as senators repeatedly echoed comments by Sen. Daniel K. Inouye, D-Hawai'i, who introduced Willard to the committee.

"I commend this wise decision," Inouye said of Willard's nomination. "He understands the geopolitical dynamics at work here (in the Pacific)."

China, Willard said, must be engaged as an ally and treated as a potential adversary.

The military buildup in China has been extraordinary, he said, and will demand a constant rethinking of the nation's Pacific strategy.

Still, diplomatic, peaceful military opportunities exist to work with the Chinese, especially on the North Korean problem, Willard said.

"We certainly see the need to leverage China," he said.

Willard also briefly touched on plans to move 8,000 Marines from Okinawa, Japan, to Guam, which has sparked debate about how to conduct such a large operation and how much it could cost.

Willard said a proposal by Rep. Neil Abercrombie, D-Hawai'i, to ensure that construction workers in Guam hired to build the necessary infrastructure are paid at Hawai'i levels, could increase the cost of the move from $10.3 billion to $15 billion.

Willard is a Los Angeles native and a 1973 graduate of the U.S. Naval Academy. He spent much of his career as an F-14 fighter jet aviator before entering the ranks of the senior naval command. He earned a master's degree in engineering management from Old Dominion University and did graduate work at the Massachusetts Institute of Technology.

The Pacific Command encompasses about half the Earth's surface, stretching from the West Coast of the U.S. to the western border of India, and from Antarctica to the North Pole.

The command oversees 36 nations, 3.4 billion people, 3,000 different languages and the world's six largest militaries — the U.S., China, India, Russia, North Korea and South Korea.

Willard's film career has been brief but notable. He was a consultant on the 1986 Tom Cruise movie "Top Gun," with a brief cameo performance. Willard piloted the Soviet fighter that received a "salute" from Cruise.

Gates announced in April that Navy Adm. Patrick M. Walsh had been nominated for reappointment to the grade of admiral and assignment to command U.S. Pacific Fleet, headquartered at Pearl Harbor.

Walsh is serving as vice chief of naval operations at the Pentagon.